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This work reports the general fabrication of hierarchical sheet/plate-like M-BDC MOFs for electrochemical non-enzymatic glucose sensing.

The self-assembly of two-dimensional (2D) nanostructures into one-dimensional (1D) nanoarchitectures may result in materials which combine the unique physicochemical properties of 2D nanostructures with the excellent charge transport properties of 1D architectures. Herein, we report the self-stacking of 2D nickel−cobalt (Ni−Co) phosphate nanoplates into 1D chainlike architectures with the assistance of metal glycerates as self-templates. This unique selfassembly process is driven by the adsorbed ethyl glycerate on the surface of the individual nanoplates, which promotes the subsequent growth of the new nanoplate on top of the previously formed nanoplate, thereby leading to the self-stacking of these nanoplates along the vertical direction. The flexibility of the proposed method is also highlighted by the feasible preparation of nickel phosphate with the same self-assembled structure. When tested as a catalyst for oxygen evolution reaction (OER) in an alkaline medium, the bimetallic Ni−Co phosphate (derived from Ni-Co-TEP) with the nanoplate-assembled chainlike structure displays much lower overpotential (η 10 = 310 mV) and Tafel slope (68 mV dec −1 ) than its pristine counterparts. The enhanced OER activity of this bimetallic catalyst may be attributed to (i) the highly interconnected structure and the bimetallic composition which promote improved charge transport; (ii) the porous chainlike structure which provides increased number of active sites, facilitates easier electrolyte infiltration, and promotes good electrical contact with the electrolyte, and (iii) the presence of Ni 3+ and Co 3+ active sites (nickel−cobalt (oxy)hydroxides) which can promote the chemisorption of OH − and facilitate electron transfer from the OH − to the surface Ni/Co sites during OER.

This work reports the fabrication of bimetallic nickel–cobalt hydrogen phosphate with unique nanotube-assembled 1D and 2D architectures for electrocatalytic OER.

Layered double hydroxides (LDHs) containing first‐row transition metals such as Fe, Co, and Ni have attracted significant interest for electrocatalysis owing to their abundance and excellent performance for the oxygen evolution reaction (OER) in alkaline media. Herein, the assembly of holey iron‐doped nickel‐cobalt layered double hydroxide (NiCo‐LDH) nanosheets (‘holey nanosheets’) is demonstrated by employing uniform Ni–Co glycerate spheres as self‐templates. Iron doping was found to increase the rate of hydrolysis of Ni–Co glycerate spheres and induce the formation of a holey interconnected sheet‐like structure with small pores (1–10 nm) and a high specific surface area (279 m2 g−1). The optimum Fe‐doped NiCo‐LDH OER catalyst showed a low overpotential of 285 mV at a current density of 10 mA cm−2 and a low Tafel slope of 62 mV dec−1. The enhanced OER activity was attributed to (i) the high specific surface area of the holey nanosheets, which increases the number of active sites, and (ii) the improved kinetics and enhanced ion transport arising from the iron doping and synergistic effects.

This work reports the first utilization of anthocyanin extracted from black rice (Oryza sativa L.) grains as a structure-directing agent for the synthesis of hollow zinc oxide (ZnO) spheres via a simple solvothermal reaction and their subsequent modifications with various amounts of multiwalled carbon nanotubes (MWCNTs). Following hybridization with MWCNTs, some MWCNTs are observed to penetrate into the inner cavities of the spheres, while ZnO nanoparticles are formed on the surface of some MWCNTs. When employed as a sulfur dioxide (SO 2 ) sensor, the ZnO−MWCNT (15:1) composite displays a high response of 156 to 70 ppm of SO 2 at an optimum temperature of 300 °C as well as good selectivity to SO 2 with the response to 50 ppm of SO 2 gas being 3 times higher than those to other gases, such as CO, CO 2 , methanol, toluene, hexane, and xylene. Interestingly, the sensing behavior of this composite is strongly influenced by the proportion of MWCNTs. Specifically, n-type sensing behavior is observed for both ZnO−MWCNT (10:1) and (15:1) composites, while p-type behavior is observed for the ZnO−MWCNT (5:1) composite. The switch in sensing behavior suggests the major contribution of p-type MWCNTs to the electronic and sensing properties of the ZnO/MWCNT composites. The density functional theory (DFT) simulations on the adsorption of SO 2 on the ZnO/CNT system reveal that the SO 2 molecule only chemically interacts with the O adatom of ZnO (i.e., oxygen atom adsorbed on the surface of ZnO) to form sulfur trioxide (SO 3 ), and charge transfer is observed from ZnO to CNT, which enhances the change in resistance of the composite sensor upon exposure to SO 2 gas.

We study the adsorption and the dissociation of O molecules on the active sites of a boron-doped pyrolyzed Fe-N-C catalyst using density functional theory. Initially, we determine the possible structure of the FeN active site of the pyrolyzed Fe-N-C catalyst doped with a boron atom by considering the presence of a nitrogen atom as a metal-free site. The most stable configuration of the structure occurs when the boron and nitrogen atoms coalesce with the FeN site forming a complex site. This structure has higher stability compared to the undoped FeN site. The doped FeN possesses the unique ability to adsorb an oxygen molecule in a side-on mode due to the presence of the boron-nitrogen pair acting as a supporting site. One O atom of the O molecule sticks strongly to the top of the iron atom, while the other binds with the boron atom. This O side-on adsorption stretches the O-O bond length by 15%. Furthermore, the examined catalyst surface can dissociate the oxygen molecule easily with only half the energy barrier of the undoped FeN structure.

Graphical abstract Research highlights Hierarchical 3D wool-ball-like ZnO nanostructures were synthesized via a solvothermal method. 3D wool-ball like ZnO/MWCNT composites with different ratios (3:1, 5:1, and 10:1) were prepared. The 3D wool-ball like ZnO/MWCNT composite showed high response and good selectivity to SO2 gas. AbstractThis work reports a facile glycerol-assisted solvothermal method for synthesizing hierarchical three-dimensional (3D) wool-ball-like zinc oxide (ZnO) nanostructures and their subsequent modifications with multi-walled carbon nanotubes (MWCNTs) as modifiers for achieving sensitive and selective detection of toxic sulfur dioxide (SO2) gas.Structurally, the as-synthesized 3D wool-ball-like ZnO is assembled of two-dimensional (2D) plate-like structures, which 3 themselves are arranged by numerous small nanoparticles. Furthermore, in this work we observed an interesting new phenomenon in which when a high concentration of MWCNTs is introduced, many small nanorods grew on the surface of the plate-like structures which assemble the 3D wool-ball-like ZnO nanostructures. When evaluated for SO2 detection, the ZnO/MWCNTs (10:1) composite (ZnO:MWCNTs= 10:1) shows a high response of 220.8 to 70 ppm of SO2 gas (approximately three times higher than the response of pure wool-ball-like ZnO) at an optimum operating temperature of 300 °C. Additionally, the composite also displays good stability and selectivity to SO2 with the response to 50 ppm of SO2 being 7-14 times higher than the responses to other tested gases at a similar concentration. The excellent sensing performance of the wool-ball-like ZnO/MWCNTs (10:1) composite is mainly attributed to: (i) the formation of p-n heterojunctions at the ZnO/MWCNTs interfaces, which greatly enhances the resistance changes upon exposure to SO2 gas and (ii) the increased amount of adsorption sites for O2 and SO2 gas molecules owing to the larger surface area of the composite and defects sites generated by the functionalization process of MWCNTs.